This application claims the priority of Japanese Patent Application Nos. 2001-251784 filed on Aug. 22, 2001 and 2001-393479 filed on Dec. 26, 2001, which are incorporated herein by reference.
The present invention relates generally to a probe opening fabricating apparatus and a near-field optical microscope using the same, and more particularly to an improved technique for controlling the dimensions of an opening at the tip of a probe.
Typical microscopes are capable of observing infinitesimal or ultrafine sites of a sample in a non-contact and non-destructive manner, and through connection with a spectrochemical analyzer, etc., have the ability to analyze not only the geometry and structure of an object to be observed but also its components, etc., allowing applications in a wide variety of fields.
The common optical microscopes are, however, incapable of observing objects smaller than the wavelength of light, posing a limit to its resolution. The reason is that light has a diffraction limit and hence could merely observe objects up to the wavelength used.
It is a near-field optical microscope using a probe which has a minute opening of the order of some tens to hundreds of nanometers for example that makes possible the observation in an ultrafine region beyond the diffraction limit.
FIG. 1 is a schematic representation of a near-field optical microscope. The nearical field optical microscope is generally designated at 10 and performs the measurement of a sample as follows. A minute sample 12 to be measured is placed on a flat substrate 14. When a light beam 18 from a light source 16 impinges on a sharpened probe 22, evanescent light 20 emerges from an opening having a diameter less than the light wavelength at the tip of the probe 22, The evanescent light 20 is localized within a region having distances less than the light wavelength from the surfaces at and near the probe tip.
At that time, if the sample surface is brought into contact with the field of the evanescent light 20 appearing on the surfaces of the probe 22, as the result of the tip of the probe 22 coming closer to the sample surface, the evanescent light 20 will scatter outside the sample surface. Part of the scattered light 21 enters the interior of the probe 22 and is directed via-a beam splitter 19 and through a spectrometer 38 to a detector 24, for data processing by a computer 26.
Thus, a stage 30 is displaced by a stage controller 28 associated with the computer 26, and a surface to be measured of the sample 12 is scanned while controlling the vertical distance between the tip of the probe 22 and the sample 12 so as to keep constant the intensity of the scattered light 21 detected by the detector 24, whereby unevenness of the sample surface can accurately be measured without contacting the sample 12. The component analysis also becomes feasible by detecting fluorescence, Raman light, etc., from the sample excited by the evanescent light 20.
The near-field optical microscope has some measurement modes. The above measurement mode is called xe2x80x9cillumination-collection modexe2x80x9d which is one of representative measurement modes superior in resolution, etc., in which incident light directed via the interior of the probe to its tip is illuminated, through the opening, on the sample as the field of evanescent light (illumination), after which scattered light having information on the sample is again directed via the minute opening at the tip into the interior of the probe, for detection (collection).
The other measurement mode for use in the measurement can be xe2x80x9cillumination modexe2x80x9d in which incident light directed via the interior of the probe to its tip is illuminated, through the opening, on the sample as the field of evanescent light, the resultant scattered light being directed via an external optical system including lenses, etc., to the detector to effect the detection.
Any microscopic regions beyond the diffraction limit can thus be measured by using as measurement light the evanescent light localized within a region having distances less than the light wavelength from the surfaces at and near the probe tip.
xe2x80x9cCollection modexe2x80x9d measurement is also carried out in which light is irradiated from the side (substrate 14 side) opposite to the sample surface to be measured so as to generate an evanescent light field in the vicinity of the sample surface to be measured, with the probe tip being brought into contact with this field to thereby scatter the evanescent light field, the resultant scattered light being collected via the opening at the probe tip, for detection.
The probe 22 as shown in FIG. 2 comprises a core 32 made of a dielectric or other material having light transmission properties, and a thin metal film mask 34 formed on the surfaces of the core 32 by vapor deposition, etc.
The mask has at its extremity an opening 36 through which a core end 32a is exposed.
Such a probe tip opening is fabricated as follows. First, an extremity of an optical fiber core is sharpened by, e.g., selective chemical etching or by thermally drawing out.
A metal is then sublimated by heating in vacuum, and deposited as a thin film on the surface of the sharpened site, to thereby form a mask of a thin metal film for example.
The mask extremity is then removed by ion cutting using focused ion beams (FIB) for example to fabricate the opening 36.
Alternatively, a metal film may be deposited from diagonal rear while rotating the probe so that only the probe tip is free from the metal film and defines an opening in conjunction with a thinner metal film portion in the vicinity thereof The opening 36 may be formed by this process.
The thus fabricated probe 22 is attached to a near-field head 31 of the near-field optical microscope 10 to effect the above near-field light measurement.
In order to improve the resolution of the near-field optical microscope, an opening having desired dimensions needs to be fabricated with a high reproducibility at the tip of the prove.
The above opening fabricating method by ion cutting provides a high controllability of the opening diameter but makes the processes extremely hard.
The above opening fabricating method by diagonal vapor deposition is incapable of providing fabrication with a high reproducibility, due to the locality problem of the vacuum evaporator.
For these reasons, the thus fabricated probe may not necessarily ensure successful measurement even though it is attached to the near-field optical microscope for measurement.
Thus, up until now, the development of technique has strongly been desired which enables the opening of desired dimensions to be fabricated with a high reproducibility at the probe tip, but there has been no proper technique capable of satisfying the requirements.
The present invention was conceived in view of the above problems involved in the prior art. It is therefore the object of the present invention to provide a probe opening fabricating apparatus capable of readily fabricating an opening of desired dimensions with a high reproducibility, as well as a near-field optical microscope using the same.
In order to attain the above object, according to the present invention there is provided an opening fabricating apparatus for creating an opening with desired dimensions at a mask tip of a near-field optical microscope probe, the probe including a core made of a material having a light transmission property and a mask formed on a surface of the core and made of a material having a ductility and a light shielding property; the apparatus comprising a light source, a reflection means, a light detection means, press means, storage means, calculation means and press control means.
The light source allows light to impinge on the probe.
The reflection means have an abutting surface which comes into abutment against the tip, the abutting surface reflecting incident light from the light source, directed via the core to the opening.
The light detection means detect the quantity of light of reflected light from a site where the tip abuts against the reflection means.
The press means performs pressing of the tip against the reflection means in the direction of the optical axis.
The storage means store in advance calibration information on the quantity of light of the reflected light and the dimensions of the opening.
The calculation means figure out the quantity of light of the reflected light for the acquisition of the opening with desired dimensions, from the calibration information stored in the storage means.
The press control means control pressing of the probe tip against the reflection means in the direction of the optical axis, effected by the press means, so as to allow the quantity of light of the reflected light detected by the light detection means to become equal to the quantity of light figured out by the calculation means.
As used herein, the core made of a material having a light transmission property refers to one made of a material such as quartz, semiconductor, CaF2, and chalcogenide or other optical fiber material.
As used herein, the mask made of a material having a ductility and a light shielding property refers to a metal thin film, etc., for use in a mirror, such as gold, aluminum, silver, chromium and titanium, deposited on the core by vacuum evaporation or the like.
As used herein, creating an opening at a probe tip mask means that due to the ductility of the mask at the probe tip, pressing of the probe tip against the reflection means in the optical axis allow the metal to be drawn out thinly to form an opening thereat, exposing the core tip from the mask opening.
As used herein, the quantity of light of the reflected light refers to the quantity of light whose value is null when the mask has no opening since the reflection means and the probe core are shielded by the mask, and whose value increases, once the mask comes to have an opening, as a function of the dimensions of the opening since the core receives via the opening the reflected light reflected by the reflection means from the surface where the reflection means abut against the probe tip.
In the probe opening fabricating apparatus of the present invention, the press means can preferably be feed means for pressing the probe tip against the reflection means in the optical axis direction such that the mask over the probe tip is gradually drawn out thinly without being torn to pieces.
A near-field optical microscope in accordance with the present invention is provided with the probe opening fabricating apparatus, the near-field optical microscope acquiring information on a surface to be measured of a sample by: (a) an illumination-collection mode in which evanescent light is illuminated on the surface to be measured of the sample, the evanescent light emerging from an opening at a probe tip which has the opening created by the opening fabricating apparatus, the resultant scattered light or reflected light being collected through the opening; or (b) an illumination mode in which evanescent light is illuminated on the surface to be measured of the sample, the evanescent light emerging from the opening at the probe tip which has the opening created by the opening fabricating apparatus, the resultant scattered light or reflected light being collected through an external optical system, or (c) a collection mode in which a field of the evanescent light appearing on the surface to be measured of the sample is scattered by the probe tip which has the opening created by the opening fabricating apparatus, the resultant scattered light being collected through the opening.
Preferably, such a near-field optical microscope further comprises an opening diameter checking mechanism for checking the dimensions of an opening at the probe tip where the opening is formed, the opening diameter checking mechanism comprising a light source, reflection means, light detection means, press means, storage means and comparison means.
The light source allows light to impinge on the probe.
The reflection means have an abutting surface which comes into abutment against the tip, the abutting surface reflecting incident light from the light source, directed via the core to the opening.
The light detection means detect the quantity of light of reflected light from a site where the tip abuts against the reflection means.
The press means performs pressing of the tip against the reflection means in the direction of the optical axis.
The storage means store in advance calibration information on the quantity of light of the reflected light and the dimensions of the opening.
The comparison means collate the quantity of light of the reflected light detected by the light detection means with the calibration information stored in the storage means, to thereby find the dimensions of the opening at the probe tip.
Preferably, such a near-field optical microscope further comprises an opening diameter adjusting mechanism for altering the dimensions of an opening at the probe tip where the opening is formed, the opening diameter adjusting mechanism comprising a light source, reflection means, light detection means, press means, storage means, setting means, calculation means and press control means.
The light source allows light to impinge on the probe.
The reflection means have an abutting surface which comes into abutment against the tip, the abutting surface reflecting incident light from the light source, directed via the core to the opening.
The light detection means detect-the quantity of light of reflected light from a site where the tip abuts against the reflection means.
The press means performs pressing of the tip against the reflection means in the direction of the optical axis.
The storage means store in advance calibration information on the quantity of light of the reflected light and the dimensions of the opening.
The setting means set desired dimensions of the opening at the probe tip.
The calculation means figure out the quantity of light of the reflected light for the acquisition of the opening having dimensions set by the setting means, from the calibration information stored in the storage means.
The press control means control pressing of the probe tip against the reflection means in the direction of the optical axis, effected by the press means, so as to allow the quantity of light of the reflected light detected by the light detection means to become equal to the quantity of light figured out by the calculation means.
In the probe opening fabricating apparatus and the near-field optical microscope using the same, the reflection means may be substituted by light emission means having an abutting surface coming into abutment against the probe tip, the light emission means being light excited by incident light from the light source, directed via the core to the opening, to thereby emit light from the abutting surface.
The excitation source for the light emission means may be voltage application means for applying DC voltage to the light emission means, in lieu of the light source, such that the light emission means emit light as a result of by voltage application by the voltage application means.